Recent studies have identified global and subset specific epigenetic alterations in AML patients with biologic and prognostic value. Recent studies have identified somatic mutations in known and putative epigenetic modifiers, including TET2, which encodes an enzyme which adds hydroxyl groups to 5-methylcytosine and leads to subsequent DNA hypomethylation. Importantly TET2 mutations are recurrent in AML and are associated with adverse outcome. These studies raise the possibility that TET2 and other mutations in epigenetic modifiers contribute to hematopoietic transformation through dysregulation of the epigenetic state in hematopoietic cells. We hypothesize that there are genetic and epigenetic alterations affecting master regulators of the epigenetic state, and that these specific alterations affect hematopoietic transformation through discrete modifications of the epigenetic state of specific target genes. We propose that TET2 is one such epigenetic regulator. We will assess the role of TET2 mutations in AML pathogenesis in studies in primary AML samples and in our novel, conditional knockout model of TET2 which implicates TET2 in stem cell self-renewal and myeloid transformation. The specific aims of this proposal will 1) assess the effects of mutant TET2 on the epigenetic state and gene expression in normal/malignant stem/progenitor cells using state-of-the-art next generation sequencing technologies. We will also 2) assess the effects of TET2 loss on myeloid transformation in vivo and develop novel, TET2-dependent AML models for biologic and therapeutic studies. Finally, given our preliminary data suggests that TET2 mutations are associated with poor outcome and increased relapse rate, we will 3) investigate the basis for the poor response of TET2-mutant AML to chemotherapy and test combination cytotoxic/epigenetic therapy as an alternate therapeutic strategy for this genetically defined subset of AML.